Velocity autocorrelation spectra in molten polymers measured by NMR modulated gradient spin-echo

¹ University of Ljubljana, FMF - Jadranska 19, 1000 Ljubljana, Slovenia, EU
² Institute Jozef Stefan - Jamova 39, 1000 Ljubljana, Slovenia, EU
³ Ilmenau University of Technology - Ilmenau, Germany, EU
⁴ Department of Biomedical Engineering, Kyung Hee University - Suwon, Korea

Received: 6 January 2014
Accepted: 4 April 2014

Abstract

The segmental dynamics in molten linear polymers is studied by the NMR method of modulated gradient spin-echo, which directly probes a spectrum of molecular velocity autocorrelation function. Diffusion spectra of mono-disperse poly(isoprene-1.4) with different molecular masses, measured in the frequency range 0.1–10 kHz at a temperature of , have a form similar to the spectrum of Rouse chain dynamics, which implicates the tube-Rouse motion as the dominant dynamic process in this frequency range. The scaling of the center-of-mass diffusion coefficient, given from the fitting parameters, changes from into at around Kuhn steps, which is less than predicted by theory and simulations, while the correlation times of the tube-Rouse mode do not follow the anticipated scaling.